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    <script>
    function A(){

    }   
    A.prototype.n=1;
    var b= new  A();
    A.prototype={
        n:2,
        m:3
    } 
    var c=new A();
    console.log(b.n,b.m);// 1 undefined
    console.log(c.n,c.m);//2,3
    </script>
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